1. Technical Field
The present invention relates generally to a tool for fitting valve keys to control valves, in particular in the manufacture of internal combustion engines and generally reciprocating piston engines with valve control.
In particular, the present invention concerns a tool for feeding, fitting and introducing valve collets or keys between valve spring retainer and valve stem of a control valve, typically the intake or exhaust valve at the cylinder head of an internal combustion engine. Such a tool is also referred by those skilled in the art as a collet or key tool and is used in a fully automatic or semi-automatic machine for cylinder head assembly.
2. State of the Art
Control valves for reciprocating piston engines are spring-loaded by a valve spring for automatic return into the closed position. That valve spring is stressed between the reference support structure of the valve, generally a cylinder head, and a valve spring plate or retainer axially held to the valve stem (referred hereinafter as: spring retainer). Especially shaped holding keys, so called valve keys, are mounted between a suitable surface in the spring retainer and annular grooves on the valve stem, for axial fixing. The spring retainer is keyed to the stem by means of such valve keys.
So-called valve key guns have long been known for manual operation for fitting the valve keys. The present invention concerns, however, in particular a special key tool for an automated machine of the general kind as described, for example, in German patent specification DE 196 52 711.
DE 196 52 711 describes a key tool of the general kind set forth for fitting valve keys to a valve of an engine. It includes an elongate guide body or holder with a longitudinal axis and an end opening through which the end of the valve stem can slightly pass into the hollow space in the holder. Arrange internally in a hollow space in the holder is a pin-like elongate core coaxially relative to the longitudinal axis. The pin has an end region which is accessible to the upper end of the valve stem. For accurately positioning the tool in the working position required for introducing the valve keys relative to the valve stem, a recess receiving the upper end is milled in the lower end region. The reference position is produced by the tool abutting with that recess against the upper end of the valve. In addition, two transport passages which are symmetrical relative to the longitudinal axis are provided in the tool in accordance with DE 196 52 711, for feeding the valve keys. The transport passages extend in the direction of the longitudinal axis externally on the core to before the end region thereof.
In contrast to the state of the art at that time, the tool in accordance with DE 196 52 711 implements the function of automatically introducing the valve keys directly into their reference position on the valve stem. Therefore, additional aids like levers or pusher members, in particular for radially supplying the keys, are not required in that tool of the general kind specified. On the one hand, adjustability of the inwardly curved end region of the transport passages is required for automatically introducing the valve keys in accordance with DE 196 52 711. On the other hand, that principle is crucially dependent upon accurate positioning of the tool relative to the valve stem as the valve keys are to be introduced with their springs directly into the annular grooves (see FIG. 5 of DE 196 52 711). A certain susceptibility to trouble is already to be expected because of tolerances in manufacture of tool and valves, when adopting the reference position on the valve itself in accordance with DE 196 52 711. In fact it is not possible to reliably guarantee in that way that the valve keys are always introduced exactly in the reference position.
Japanese laid-open specification JP 61 038831 describes a further solution which manages without typical levers or pusher members for radially supplying the keys. The device of JP 61 038831 has a tool having a moveable core comprising two sleeves and push rods which are telescopically displaceable relative to each other and relative to the stationary holder. The outer push rod can receive or release the valve stem, as a hollow cylinder. The inner push rod is guided in the outer push rod and serves for determining the position. After release of the annular grooves on the valve stem by the outer push rod the keys are firstly coarsely fed and then precisely moved or inserted into the annular grooves by a return movement of the outer push rod by means of its especially shaped lower end. Susceptibility to error is also to be expected in a tool in accordance with JP 61 038831 because of the number of parts which are actuated and which have to be adjusted.
It will be appreciated that, considered from an economic point of view, a high level of reliability, that is to say low fault susceptibility, of tools and machines used is required quite generally in industrial manufacture and especially in automobile engine building. It is only in that way that the desired high production cycle rates can be achieved as permanently as possible and expenses caused by interruptions and wastage is avoided.